The present invention relates to a digital video signal processor for a high definition television (HDTV), and more particularly, to a digital video decoding apparatus for a HDTV which allows a decoding performance with respect to a profile having larger than the bandwidth which can be processed by the decoding apparatus, by reducing the calculating amount concerning the restoration of discrete cosine transform (DCT) coefficients.
In general, a frame of a digital video signal is composed of an I-frame for processing compressed video data by using purely spatial transform without motion compensation, a P-frame for processing compressed video data by motion compensation using a forward motion vector, and a B-frame for performing more efficient video compression by selectively using a forward motion vector or a backward motion vector.
A recently standardized digital motion picture coding method has been widely adopted in various fields such as a video phone, CD-I (compact disk-interactive), DBS or ATV (advanced television).
Among various digital motion picture coding methods, the specifications for H.261 and (moving picture experts group) MPEG I are determined and are actively used in various fields. Recently, moving picture experts Group (MPEG) II has been proposed and is about to be settled.
A conventional digital video decoder for a HDTV will be described with reference to the accompanying drawings.
As shown in FIG. 1, the conventional digital video decoder for HDTV performs variable length decoding in a variable length decoder (VLD) with respect to input compressed video data (bit stream), thereby obtaining DCT coefficient information and motion vector and information on motion vector and picture coding relating to I-, P- and B-frames to then be restored into an original code value.
The DCT coefficient information passes through a inverse zigzag scan decoder (IZZ) 2, an inverse quantizer 3, and an inverse DCT 4 to be restored as pixel information. In the case of an I-frame, the pixel information is stored in a frame memory 5 using picture coding information. In the case of a P-frame or a B-frame, the current picture (restored video data) is constituted by the information obtained by adding the previous pixel information stored in frame memory 5 with the pixel information compensated in a motion compensator 6 using the motion vector obtained in the variable length coding step.
At this time, unless an error is generated during the picture restoration step, the frame memory picture of an encoder becomes the same as the frame memory value of a decoder.
The picture stored in frame memory 5 is output via a display memory (not shown) to be displayed in the different sequence according to types of pictures.
FIG. 1 shows a digital video decoder for a HDTV in general motion picture coding techniques.
According to the conventional digital video decoder, compressed video data having a bit rate lower than the bandwidth capable by the decoder can be processed without a serious problem. However, it is impossible to process the compressed video data generated from the picture having an amplitude larger than that capable by the decoder, due to the hardware capability of the decoder and limited memory.
In other words, as to the compatibility of compressed video data with a decoder, which can be widely adopted in various applicable fields, the MPEG II standards specify the syntactic properties of the compressed video data which can be decoded by the decoder and restrictive conditions of pictures to be processed, by using various profiles and levels.
The profiles and levels of the compressed video data to be actively used by MPEG II are a main profile and main level (MP@ML) adoptable for DBS and VOD (video on demand), and a main profile and high level (MP@HL) adoptable for HDTVs.
These two types of compressed video data are the same with each other in the syntactic properties but are different in the restrictive conditions for the pictures to be processed. Specifically, the amplitudes of the coded pictures are different.
For example, the maximum picture adopted for HDTV (MP@HL) is 1920.times.1152 and 60 frames/sec, and the maximum picture adopted for DBS is 720.times.576 and 30 frames/sec.
As shown in FIG. 2 which tabulates the compatibility between a number of decoders and compressed video data of assorted profiles and levels in MPEG II, the decoder for supporting the compressed video data of upper levels in the same profile should decode the compressed video data of lower levels as well as that of its own level.
In this manner, in decoding the compressed video data having different levels in the same profile, the decoder for supporting the compressed video data of upper levels can accommodate that of lower levels, but not that of higher levels.
In other words, forward compatibility is assured but backward compatibility is not.